System for remote selection of voltage level



May 22, 1956 H. E. PlNNEY 2,747,157

SYSTEM FOR REMOTE SELECTION OF VOLTAGE LEVEL Filed July 18, 1955 UnitedStates atent SYSTEM FOR REMOTE SELECTION OF VOLTAGE LEVEL Harold E.Pinney, Pittstield, Mass., assignor to General Electric Company, acorporation of New York Application July 18, 1955, Serial No. 522,472

5 Claims. (Cl. 323'43.5)

This invention relates to electrical transformer systems, and more inparticular to an improved system for remote control of the voltage levelof a variable transformer, such as a load tap changing transformer.

In a conventional load tap changing transformer system, a voltageregulating relay is commonly employed to energize the tap changing motordrive. The coil of the voltage regulating relay is generally connectedin series with the secondary winding of a potential transformer, and theprimary winding of the potential transformer is connected in parallelwith the secondary winding of the load tap changing transformer. Thecontact arm of the voltage regulating relay is spring loaded so that adecrease in voltage of the secondary winding of the load tap changingtransformer results in contacting of one set of contacts of the voltageregulating relay to energize the motor drive to make tap changes raisingthe load tap changing transformer secondary windin'g voltage, and anincrease in voltage of the secondary winding of the load tap changingtransformer results in contacting of another set of contacts of thevoltage regulating relay thereby energizing the motor drive to make tapchanges lowering the load tap changing transformer secondary windingvoltage.

It is frequently desirable to provide means for varying the voltagelevel at which the voltage regulating relay contacts close, and thecommon adjustment to accomplish this function is in the form of a screwwhich adjusts the tension of the spring on the contact arm of thevoltage regulating relay. In order to adjust the voltage level in thismanner, however, it is necessary for an operator to be physicallypresent at the location of the load tap changing transformer. In someinstances it is more desirable to be able to control the voltage levelof the voltage regulating relay from a remote position, and in order toachieve this result, in the past such adjustment has been provided by aremotely located rheostat wired in series with the coil of the voltageregulating relay. When a remote rheostat is connected in such a manner,however, any accidental open circuit of the wires connecting therheostat to the coil of the voltage regulating relay will result incomplete loss of control of tap changes of the load tap changingtransformer, and the motor drive will continuously operate the tapchanging mechanism until a limit switch has been contacted.

Another disadvantage occasioned by the use of a remotely locatedrheostat connected in series with the coil of the voltage regulatingrelay is that a temperature error may result if the resistance of therheostat is too great. in such a system, however, the resistance of therheostat must he suilieiently great with respect to the resistance ofthe wires connecting the rheostat through the voltage regulating relaycoil so that a sufficient amount of adjustment is obtainable. If thedistance between the load tap changing transformer and the remoterheostat is very great it is readily seen that such a series connectionbeice tween the coil of the voltage regulator relay and the rheostatwill be impractical due to the errors that may result.

It is therefore an object of this invention to provide an improvedsystem for the remote control of voltage level 'of a variabletransformer system.

It is also an object of means in load tap changing transformer systemfor minimizing the errors that may result from remote adjustment ofvoltage level.

A further object of this invention is to provide improved means forremote adjustment of the voltage level of a load tap changingtransformer system wherein an open circuit between the load tap changingtransformer and the remote control does not result in complete loss ofcontrol of the voltage level, and also wherein the voltage level issubstantially independent of temperature variations.

Briefly stated, in accordance with one aspect of my invention, I employa resistance, which may be variable, in series with the coil of thevoltage regulating relay of a conventional load tap changing transformersystem. This resistor is preferably located in the same location as thevoltage regulating relay. The secondary winding of a current transformeris connected in parallel with the resistor, and the primary Winding ofthe current transformer is connected in series with a substantiallyconstant source of potential and remotely located variable resistancemeans for controlling the current flowing through the primary windingsof the current transformer. The current transformer and thesubstantially constant source of potential are preferably located in thesame location as the load tap changing transformer. The potential sourcemay be an auxiliary potential transformer connected across the secondarywinding of the load tap changing transformer. The circuit components areso selected that the resistor in series with the coil of the voltageregulating relay is very small with respect to the resistance that wouldbe required for a rheostat connected in the same position to provide thesame voltage level adjustment. It is important that the resistance ofthe resistor in series with the coil of the voltage regulating relay bevery small since the greater resistance, used, the larger thetemperature error will be.

My invention will be better understood from the following descriptiontaken in connection with the accompanying drawing and its scope will bepointed out in the appended claims.

The drawing is a circuit diagram of a load tap changing transformerembodying the remote voltage level control of my invention.

Referring now to the drawing therein is illustrated a load tap changingtransformer 19 having its primary winding 11 connected to alternatingcurrent supply lines 12 and its tapped secondary winding 13 connected toa load 14 by way of lines 15 and 16. A voltage regulating relay 17 isprovided having its coil 18 connected in series with a variable resistor19, load drop compensating reactor 20 and resistor 21 and the secondarywindings 22 of a potential transformer 23. The primary winding 24 ofpotential transformer 23 is connected parallel with the secondarywinding 13 of the load tap changing transformer lit. A currenttransformer 25 inductively coupled to the line 16 has one end of itssecondary winding connected to the tap on the load drop compensatingreactor 20 and the other end of its secondary winding connected to a tapon resistor 21.

A reversible motor 30 has its shaft mechanically coupled by conventionalmeans to the tap changing arm 31 of load tap changing transformer 10.The motor has a pair of windings 32 and 33 and a lead common to the twowindings is connected to a source of potential 34. The other ends of thetwo windings 32 and 33 of motor are connected by way of contacts 35 and36 respectively to the other terminal of source of potential 34. Thesecontacts are the raise and lower contacts of voltage regulating relay17, and are bridged in the conventional manner by means of the arm 37 ofvoltage regulating relay 17.

A remote selector switch 40 connects line 41 to line 42 or to one end ofresistor 43, resistor 44, or rheostat 45, the other ends of resistors 43and 44 and rheostat 45 being connected to line 42. The remote selectorswitch 40 serves to select the desired resistance appearing in serieswith calibrating resistor 46 the primary winding 47 of a currenttransformer 48 and the primary winding 49 of auxiliary potentialtransformer 50. The re sistors 51 and 52 in lines 41 and 42 respectivelyrepre sent the resistance of these lines. The secondary winding 53 ofcurrent transformer 48 is connected in arallel with variable resistor19. The primary winding 54 of the auxiliary potential transformer may beconnected in parallel with the secondary winding 22 of potentialtransformer 23, or it may be connected in parallel with the tappedsecondary winding 13 of load tap changing transformer 10.

A remote-local switch 60, shown in the drawing in the remote position,may be provided in order to obtain control of the voltage level at thelocation of the load tap changing transformer. This switch is in serieswith the line 41 in the remote position, and in the local positionconnects line 41 to the arm of a local selector switch 61. The localselector switch 61 connects line 41 to 42 directly or by way of resistor62, resistor 63, or rheostat 64. A variable resistor 65 is connected inseries with the arm of the local selector switch 61 in order tocompensate for the effect of the line resistances 51 and 52 so that theresistor 62, 63 and rheostat 64 may be selected to have values equal tothe resistance of resistor 43, resistor 44 and rheostat 45 respectively.

In operation with the switch 60 in the remote position, the magnitude ofcurrent flowing through the primary winding 47 of current transformer 48is determined by the position of the remote selector switch 40, or inother words the voltage delivered by the secondary winding 49 ofauxiliary potential transformer causes a current to flow through theprimary winding 47 of current transformer 48 that is dependent upon theimpedance of the loop. The current induced in the secondary winding 53of current transformer 48 flows through the resistor 19, which is inseries with the coil of the voltage regulating relay. Since changing ofthe voltage drop across the resistor 19 changes the voltage level heldby the voltage regulating relay 17, the voltage level may be changed bychanging the current in the primary winding 47 of current transformer48. When the line 41 is connected directly to the line 42 the maximumcurrent will flow through the primary winding 47 of current transformer48 and therefore the maximum voltage drop appears across the resistor19. Since an increase in the voltage drop across resistor 19 of the samephase as the voltage drop thereacross produced by current of thepotential transformer 23 has the same effect on the coil of the voltageregulating relay as an increase in the secondary winding voltage of loadtap changing transformer, the voltage regulating relay actuates the tapchanging mechanism to lower the output voltage of the tap changingtransformer. A position may be provided on the remote selector switch 40to open the circuit between lines 41 and 42 and this will result in thehighest obtainable voltage level of the secondary Winding of the loadtap changing transformer. Intermediate voltage levels may be provided bymeans of the fixed resistors 43 or 44, or the voltage level may becontinuously variable by means of rheostat 45.

If the terminals of one winding of the current transformer 48 arereversed, the voltage drop across the resistor 19 due to the current ofthe winding 53 of the current transformer will buck the voltage of thepotential transformer secondary winding. In this event an open circuitof the lines 41 and 42 will result in the lowest obtainable voltagelevel and a direct connection between the lines 41 and 42 will result inthe highest obtainable voltage level.

By means of the above-disclosed circuit the resistance in series withthe coil of the voltage regulating relay may be reduced to a minimumvalue by correspondingly increasing the current output of the currenttransformer 48. This results in minimizing the effect of temperatureerror in the resistor 19. It is obvious that the minimum value of theresistor 19 is not determined by the value of the resistances 51 and 52of the lines connecting the load tap changing transformer to the remotecontrol circuit. If one of the lines 41 or 42 is open-eircuited, theload tap changing transformer will seek a voltage level determined bythe resistance of the resistor 19, and will thus not continuously rununtil it reaches a limit.

Similar control over the voltage level of the load tap changingtransformer may be provided at the location of the load tap changingtransformer, when the switch 60 is in the local position, by means ofthe local selector switch 61.

It will be understood, of course, that while the form of the inventionherein shown and described constitutes a preferred embodiment of myinvention, it is not intended herein to illustrate all of the possibleequivalent forms or ramifications thereof. It will also be understoodthat the words used are words of description rather than of limitation,and that various changes may be made with out departing from the spiritor scope of the invention herein disclosed, and it is aimed in theappended claims to cover all such changes as fall within the true spiritand scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. Means for remotely controlling the voltage level of a variableelectrical transformer system of the type employing a voltage regulatingrelay responsive to the winding voltage of the variable transformer toactuate a motor drive for controlling the voltage of the variabletransformer comprising a voltage regulating relay having a coil coupledto a winding of said variable transformer, a first resistor in serieswith said coil, and circuit means including a substantially constantsource of potential and variable resistor means connected in parallelwith said first resistor for controlling the current flowing throughsaid first resistor.

2. Means for remotely controlling the voltage level of a variableelectrical transformer system of the type employing a voltage regulatingrelay responsive to the winding voltage of a variable transformer toactuate a motor drive means for controlling the voltage of the variabletransformer comprising a voltage regulating relay having a coilinductively coupled to the secondary winding of said variabletransformer, a first resistor connected in series with said coil, andcircuit means including a substantially constant source of potential andvariable resistance means positioned at a distance from said variabletransformer connected in parallel with said first resistor for providinga controlled flow of current through said first resistor.

3. Means for remotely controlling the voltage level of a variableelectrical transformer system of the type employing a voltage regulatingrelay responsive to the winding voltage of a variable transformer toactuate a motor drive means for controlling the voltage of the variabletransformer comprising a voltage regulating relay having a coilinductively coupled to the secondary winding of said variabletransformer, a first resistor connected in series with said relay coil,:1 current transformer having a secondary winding connected in parallelwith said first resistor, and a substantially constant source ofalternating potential and a variable resistance means connected inseries with the primary winding of said current transformer to provide acontrolled flow of current through said primary winding, said variableresistor means being positioned at a distance from said variabletransformer.

4. Means for remotely controlling the voltage level of a variableelectrical transformer system of the type employing a voltage regulatingrelay responsive to the winding voltage of a variable transformer toactuate a motor drive means for controlling the voltage of the variabletransformer comprising a voltage regulating relay having a coilinductively coupled to the secondary winding of said variabletransformer, a first van'able resistor connected in series with saidrelay coil, and a current transformer having a secondary Windingconnected in parallel with said first variable resistor, a substantiallyconstant source of alternating potential and a second variable resistormeans connected in series with the primary Winding of said currenttransformer to provide a controlled flow of current through said primarycurrent transformer winding, said second variable resistor means beingpositioned at a distance from said variable transformer, said voltageregulating relay having contacts to selectively operate said motor drivemeans to raise or lower the secondary winding voltage of said variabletransformer.

5. Means for remotely controlling the voltage level of a tap changingtransformer system of the type employin g a voltage regulating relayresponsive to the load voltage of a tap changing transformer to actuatea motor drive means for maintaining the load voltage of said tapchanging transformer at a constant value comprising a voltage regulatingrelay having a coil inductively coupled to the secondary Winding of saidtap changing transformer, a first variable resistor connected in serieswith said relay coil, a current transformer having a secondary windingconnected in parallel with said first variable resister and a primarywinding connected in series with the secondary winding of a potentialtransformer and second variable resistor means, the primary winding ofsaid potential transformer being connected to the secondary winding ofsaid tap changing transformer, said second variable resistor means beingpositioned at a distance from said tap changing transformer to provideremote control of the current flowing through the primary winding ofsaid current transformer, and contacts on said voltage regulating relayto selectively operate said motor drive means to raise or lower thesecondary win-ding voltage of said variable transformer.

No references cited.

